Wound core reactor



Sept. 26, 1944. L, w FOSTER 2,359,102

WOUND CORE REACTOR Filed Nov. 5, 1940 Inverter": I Levin \N. Foster;

His Attorney.

Patented Sept. 26, 1944 WOUND CORE REACTOR Levin W. Foster, Pittafleld, Mass, assignor to General Electric Company, a corporation of New York Application November 5, 1940, Serial No. 364,398 2 Claims. (Cl. 175-356) My invention relates to electromagnetic induction apparatus, and particularly concerns reactors. I

It is an object of my invention to provide a low loss inductive reactor which may be used in high power alternating current circuits and which may be fabricated by rapid economical manufacturing operations. Other and further objects and advantages will become apparent as the description proceeds.

In carrying out my invention in its preferred form, I provide an electrical winding structure which may consist of a preformed form-wound copper winding having a pair of straight winding legs, each of the winding legs being surrounded by a magnetic core in hollow cylindrical form composed of many turns of strip material, wound flatwise, one over the other, and each closely embracing the underlying turn. In order to make the inductance of the electrical winding substantially constant over a reasonable range of current values, air gaps are provided in each of the cores. The air gaps are formed by slitting the strip material. The cores are arranged with the air gaps inside the opening or window of the winding structure for the purpose of keeping magnetic losses at a minimum.

A better understanding of my invention will be afforded by the following detailed description considered in connection with the accompanying drawing, and those features of the invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. In the drawing, Fig. l is a cross sectional view of an embodiment of my invention showing an electromagnetic induction device in one stage of the manufacturing operation, together with a clamping mechanism for holding the turns of strip during the air gap slitting operation. Fig. 2 is a cross sectional view showing the electromagnetic induction device of Fig. 1 in completed form and mounted within an enclosing tank for insulating fluid such as oil. Fig. 3 is a fragmentary view of one of the cores with a modified fastening means therefor. Fig. 4 is another fragmentary view showing a different modification of the arrangement of Fig. 3. Like reference characters are utilized throughout the drawing to designate like. parts.

The electromagnetic induction device shown in the drawing by way of illustration consists of a winding structure I I and a pair of magnetic cores l2 and I3. In the case of a reactor, the winding structure ll consists of a continuous coil or winding of wire composed of suitable conducting malegs I and I5.

terial such as copper, together with suitable insulation. Although particular reference is made in the specification to reactors, it will be understood that my invention is not limited thereto and does not exclude transformers which for certain applications may advantageously be constructed with air gaps in their cores. The winding structure ll may be a form-wound winding which is fully preformed and completely insulated before the application of the magnetic cores to the winding legs.

The cores i2 and it are composed of wound strip magnetic material and may be of the type disclosed in United States Patent 2,160,588, Graniield. For the sake of obtaining as high space factor as possible the winding structure H is preferably formed with winding legs i4 and I5, which are straight for a distance corresponding to the axial length of the wound strip cores l2 and II which are of hollow cylindrical form and closely embrace the winding legs.

For eliminating saturation effects, and making the inductance of the winding substantially constant up to a reasonable maximum value of current flowing therein, the cores I2 and ii are provlded with air gaps i6 and I1 respectively, as shown in Fig. 2 in the finished reactor. The gaps It and I! are relatively narrow having small dimensions in relation to the conductive winding The cores l2 and iii are arranged with the air gaps It and I1 inward or towards each other so that they come within the winding window it. For the purpose of insulation and cooling, the reactor may be immersed in oil or other suitable insulating liquid l9 and to this end, an enclosing tank 20 i preferably provided. The tank 20 may be composed of cast iron or fabricated sheet steel such as the transformer and reactor tanks already in common use.

The use of a magnetic core composed of turns of strip, each closely embracing the underlying turn and composed of suitable low loss magneti material such as 3 per cent cold rolled silicon steel as disclosed more in detail in the Granfield v patent, results in high magnetic efficiency with low magnetic loss in the cores l2 and I3. By arranging the air gaps I6 and i1 within the winding window i8, magnetic fringing or spreading of the leakage flux crossing the air gaps l6 and I1 is reduced to a minimum, and such leakage flux as is produced flows through an air path within the winding window l8 instead of entering the material of which the tank 20 is composed. Since the tank Zll can not readily be composed of laminated magnetic material, and it would in any event be prohibitive to attempt to construct it of low loss magnetic material, it is highly desirable to prevent the entry of any magnetic flux into the tank from' the magnetic circuit of the reactor. It would, of course, be too costly to utilize a non-magnetic tank such as one composed of copper, and furthermore, even in cases where no tank is employed, it is desirable to use a reactor core construction in which there is a minimum tendency for the leakage flux of the reactor to travel in a path outside the reactor as it is desirable to minimize any possibility of interaction between the reactor and external magnetic fields or between the reactor and apparatus which may be affected by fields from the reactor. Owing to the low core losses of my construction, it may be used to good advantage in power reactors, e. g., those rated at 10 k. v. a. and above.

The magnetic strip material ma be applied tothe winding legs i4 and I5 in the manner described in the aforesaid Granfield patent. Briefly, this consists of winding magnetic strip material on to mandrels so as to give the coil of strip so wound the size and shape which it is to have in the finished electromagnetic induction apparatus, heat-treating the strip material in this form to eliminate strains, give it a set in the desired shape and improve the magnetic properties, and thereafter unwinding from the original coil of strip and rewinding around the winding leg with the turns of strip in the same sequence in the core, assembled with the winding, as in the original coil of magnetic strip. The magnetic strip material is then readily collapsed to its original shape, leaving it in a strain-free condition, which results in low magnetic losses as explained in the Granfield patent.

- In order to provide the air gaps in the core without introducing any objectionable strain in the portion of the strip-adjacent the air gaps, the air gaps are preferably cut in the finished coils of strip by means of a milling cutter or saw, although a shaper may also be employed. For holding the coil during the operation of cutting the air gap and to prevent the turns of strip from separating during the operation, a clamp of any suitable type such as the clamp 2| may be provided, having a pair of jaws 22 shaped to fit the outer surface of the core and separated sufliciently at 23 to permit the use of the milling cutter or other tool for cutting the air gap H. The assembled unit consisting of the winding structure II and the applied cores i2 and i3 is placed within the clamp 21 with the jaws 22 gripping one of the cores, e. g., the core IS. The air gap i1 is then cut. The gap is cut with parallel sides to make the gap length uniform for all the layers of strip in order that some layers of strip will not saturate before others and produce high losses. Preferably the construction of the winding structure H is such that danger of injuring the insulation thereof by the milling cutter is eliminated. For example, there may be a fiat side 24 with a block 25 of suitable material, such as hard wood, temporarily or permanently inserted between the fiat side 24 and the inside surface of the portion of the core where the air gap I1 is to be out. After the air gap I! has been cut, the jaws 22 and the clamp 2| are released, and the core [3 is turned around to the position shown in Fig. 2, having the air gap ll within the winding window I-8 of the winding structure l I. It will be understood thata similar procedure is followed in cutting the air gap 16 and bringing it vwithin the winding window Hi. This procedure makes it possible to produce the construction illustrated although the cores each have only a single air gap and the air gap is too narrow to permit slipping the winding leg through the air gap in order to assemble the core with the conductive-winding structure.

Since the turns of strip of the cores l2 and I3 have a permanent set, no difficulty is experienced in retaining the shapes of the cores after the air gaps l6 and i1 have been cut and the air gaps have been brought to the position shown in Fig. 2. However, for the sake of providing, rigidity of core structure under adverse conditions, the strip material is preferably fastened in place after the cores have been turned with the air gaps within the winding window. If desired, a non-magnetic block 26 may be inserted in the air gap after it is cut and a strap 21 of non-magnetic material may be secured as by welding or riveting to the core over the block 26, as shown in Fig. 3. This may be done before the jaws 22 and the clamp 2i are released. In this case, however, it will be necessary to provide suificient clearance between the winding leg and the inside surface of the core to permit rotating the core to the position shown in Fig. 2. Instead of using the block 26 and the strap 21, one may also secure the adjacent turns of strap to each other by a suitable means such as a simple rivet on either side of the portion of the strip where the air gap is to be cut, or one may run a pair of line welds 28 and 29 across the edges of the strip on one side of the core, as shown in Fig. 4. The welds 28 and 29 may be made on either side of the sec-- tion where the air gap I1 is to be out. It will be understood, however, that in employing rivets or line ,welds careis to be taken that both line welds or rivets are in the same plane perpendicular to the cylinder axis of the core in order to prevent any eddy current path or short circuit in the turns of strip.

While I have shown particular forms of electro-magnetic induction apparatus embodying my invention and have illustrated a particular mechanism, there may be many changes and modifications without departing from the spirit and scope of my invention, and I aim in the appended claims to cover such changes and modifications.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A reactor comprising a conductive winding structure and a magnetic core, the winding structure having a winding leg surrounded by said core and a window or opening through which one side of the core passes, said core being composed of magnetic strip material closely wound spirally fiatwise and having a single relatively narrow air gap therein within the winding window to eliminate excessive magnetic losses, said air gap being of small dimensions in relation to said windmg leg, and means adjacent said 'gap for attachmg adjacent turns of said magnetic strip material.

2. A method of assembling a magnetic core with a winding structure to form a low-loss power reactor, which comprises winding magnetic strip material through an opening in the winding structure and around the winding leg thereof to form a core, passing a cutting tool through an outer side of said core to form an air gap therein and rotating the core to bring the air gap within the window in the winding structure to eliminate spreading of magnetic fiux induced in the core by current passing through the winding structure.

- 1 LEVIN W. FOSTER. 

